so this worked pretty much perfect. while mashing the first batch I heated up as much water as i could fit in my cube cooler to about 140-150F. After this I drained my first batch into the now empty kettle and then put the remainder of my 2nd batch strike water in my 5 gal kettle and brought this up to a boil. mixed them together in the mash tun when the first batch was done draining and I was pretty close to where I needed the strike water to be.
Awesome, glad it worked. I am not sure I will ever take on a double brewday, just too much to do!